How to set up a render farm
To setup a render farm you need multiple computers that can talk to each other over a network. Then you setup one as a master and the others as slaves that will get their workload from the master.

Blender includes a network render addon that just needs to be enabled in preferences then configured on each machine.

Flamenco is the new network render project being worked on.

For a small farm you can also manually start blender on each machine, giving each a different range of frames to render. With *nix machines this can be done through an ssh connection with blender -b myscene.blend -s 1 -e 10 -a, this can be expanded to a script that can automate sending the command to each machine for you.